I have this problem resolved.
Affected iphone 6 ios 10.1.1
Not affected iphone se 10.1.1
Exchange 2003 self signed cert
Attempts to repair
Reset network settings - no luck
Reset all settings - no luck
Restore phone from backup - no luck
4 hours with apple support, up to senior uk advisor. No answer just that they had not seen this problem before and I appeared to be the only person with this problem so its not a bug !!!!
Every time verifying details had certificate warning but no continue button just option for cancel and details.
Iphone SE prompted for certificate warning but had options for cancel, details and continue.
This has something to do with the ssl security settings / certificates but this fix works.
So on first page of add exchange account add email and password as normal. This brings you to second page.
KEY change your email address to name@externalipaddress not firstname.lastname@example.org then add the server IP in the box. Leave domain blank. Add your username as just "name" not "email@example.com" . Thats the login name for your exchange account not your email address. You will then get the certificate warning but now you will have a continue button that was missing before. Just continue and this should work and get all ticks. If you have problems sending mail go back and add the domain in the correct field.
This is an unusual way to make the settings work but then when i go back and check the exchange account settings ios has changed the email from name@externalipaddress to the correct setting firstname.lastname@example.org.
So i think this is a bug and would like to hear from apple why this works but dont think i will ever get an answer.
Hope you get working.